It is sometimes very difficult to know whether a nest is occupied continuously by the same colony, or by one dying out, closely followed by robbing, followed by a new swarm moving in. We have a colony that "has been living in the church roof for 20 years" - I saw a swarm go in last summer. At the moment it looks extremely busy, but on closer inspection you see that no pollen is going in at all....it is a dead nest being robbed out. There is a very good chance that a swarm will re-occupy it in the near future, and as far as most people are concerned, that colony will be on it's 21st year!
Bees are attracted to burnt areas/chimneys though....I guess they know best.
As far as the soot is concerned, surely the type of fuel burned must have some bearing on it's composition....seasoned wood/unseasoned wood/coal/anthracite etc etc? Personally, I'd have thought that there was much difference between living in a chimney and having soot pourred over.....couldn't the very fine particles of soot block spiracles? My gut feeling is that this wouldn't be a very good idea.
Try it on your own bees, and let us know how you get on! I'm sceptical, but would be delighted if it were proven to be a useful treatment.